Technical Field
The invention relates to a semiconductor device and a manufacturing method thereof, and particularly relates to a semiconductor transistor and a flash memory and a manufacturing method thereof.
Related Art
Since a non-volatile memory is capable of implementing data storage, data reading and data erasing operations for multiple times, and data stored therein is not disappeared after power-off, the non-volatile memory is widely used in personal computers and electronic equipment.
A typical non-volatile memory includes a memory cell region and a peripheral circuit region. In the memory cell region, a plurality of memory units and standard operating voltage transistors as switch transistors are disposed. In the peripheral circuit region, various semiconductor transistors with different operation voltages are disposed according to an actual requirement. Generally, a plurality of standard operating voltage transistors (core transistors), a plurality of middle operating voltage transistors or high operating voltage transistors are disposed in the peripheral circuit region. The semiconductor transistors with different operation voltages are required to have different structures according to electrical performances thereof.
However, in the typical non-volatile memory, the memory units, the standard operating voltage transistors, and middle operating voltage transistors and/or high operating voltage transistors are formed together in a same manufacturing process. Regarding a middle operating voltage transistor or a high operating voltage transistor, in order to avoid generating a leakage current, a lightly doped drain (LDD) structure with a large width is formed in a substrate between a source/drain region and a gate.
Taking an NAND flash memory as an example, during the manufacturing process, the middle operating voltage transistors or the high operating voltage transistors are not easy to get a wide LDD, so that a offset a spacer overlay margin is required, i.e. an extra lithography etching process is needed to widen the LDD of the middle operating voltage transistors or the high operating voltage transistors. Taking an embedded flash memory as an example, in the manufacturing process, the width of the LDD of the middle operating voltage transistor or the high operating voltage transistor can be determined by a width of the spacer of the middle operating voltage transistor or the high operating voltage transistor, and the width of the spacer is influenced by a height of the gate. In case that a height the gate of the middle operating voltage transistor or the high operating voltage transistor is lower than a height of the stacked gate structure of the memory unit or a height of a gate of the standard operating voltage transistor, the wide LDD cannot be achieved, which influences properties of the semiconductor device.